Variable resistor with vernier drive



June 11, 1968 w, W 3,388,365

VARIABLE RESIST OR WITH VERNIER DRIVE Filed July 25, 1967 25 f f'l g 96.- IN I 4/84 88V ---.?0 66 I l 52 58 87 2 INVENTOR GEORGE W WOOD AT TOR/V5) United States Patent 3,386,365 VARIABLE RESISTGR WITH VERNIER DRIVE George W. Wood, Hammonton, Nl, assignor to IRC, Inc, Philadelphia, Pa. Filed July 25, 1967, Ser. No. 655,949 8 Claims. (Cl. 338-162) ABTRACT OF THE DES CLQS A variable resistor comprising a flat, rectangular housing, having one rounded corner and an enclosed cavity. A resistance element having an annular resistance path is mounted within the housing. A shaft is rotatably supported within the cavity for rotation about the axis of the annular resistance path. A contact is carried by the shaft and slidably engages the resistance path. A drive Wheel is rotatably supported in the housing and extends through an opening in the rounded corner of the housing to permit rotation of the drive wheel. A first drive connection is provided between the drive wheel and the shaft whereby rotation of the drive wheel rotates the shaft only a fraction of the amount that the drive wheel rotates. A second drive connection is provided between the drive wheel and the shaft whereby rotation of the drive wheel rotates the shaft substantially the same amount. The drive wheel is movable between a position in which the first drive connection is operable and a position in which the second drive connection is operable. This provides a vernier drive in which the second drive connection provides rough adjustments of the variable resistor and the first drive connection provides fine adjustments.

Background With the trend to miniaturization of electrical components, there has been developed several types of miniature variable electrical resistors. One such miniature variable resistor is the type shown in United States Letters Patent No. 3,127,583, issued Mar. 31, 1964, to M. W. Hudson et all, entitled Variable Resistor. This type of variable resistor in general comprises a flat, substantially rectangular, housing having an enclosed cylindrical cavity therein. An annular resistance element is mounted within the cavity for rotation about an axis which is on the axis of the annules of the resistance element. A contact is carried by the gear and slidably contacts the resistance element so that rotation of the gear moves the contact along the resistance element. A drive shaft is rotatably mounted in the housing and projects beyond a side edge of the housing so that it is exposed for rotation. The drive shaft has a worm gear thereon which meshes with the gear so that rotation of the shaft rotates the gear.

In this type of variable resistor, the purpose of the gear drive is to require a number of turns of the drive shaft to move the contact along the resistance element. Thus, the contact is moved along the resistance element in small increments so that an accurate setting of the contact on the resistance element can be easily obtained. This permits the achievement of accurate resistance values in a miniaturized variable resistor. However, one problem with this type of variable resistor is that to achieve a large change in the resistance value setting of the variable resistor is a time-consuming operation in that it requires a great number of turns of the drive shaft to achieve the change. Therefore, it would be desirable to have such a miniaturized, variable resistor which provides for ease of achieving large changes in the resistance setting of the variable resistor, as well as permitting small increments of change.

3,388,365 Patented June 11, 1968 ice Summary of invention It is an object of the present invention to provide a novel variable electrical resistor.

It is another object of the present invention to provide a variable electrical resistor having a vernier drive to the contact so as to permit rough and fine adjustments of the position of the contact along the resistance element.

It is a further object of the present invention to provide a variable resistor having a drive wheel for moving a contact along a resistance element, a first drive connection between the drive wheel and the contact which moves the contact by small increments along the resistance element and a second drive connection between the drive wheel and the contact which moves the contact by large increments along the resistance element.

Other objects will appear hereinafter.

Brief description of drawing For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIGURE 1 is a perspective view of the variable resistor of the present invention.

FIGURE 2 is a sectional view taken along line 2-2 of FIGURE 1.

FIGURE 3 is an exploded perspective view of the parts of the variable resistor which are within the housing.

Referring to the drawing, the variable resistor of the present invention is generally designated as 10. Variable resistor 10 comprises a fiat, substantial square housing 12 which has one rounded corner. Housing 12 includes a bottom section 14 and a cover 16 fitting on and secured to the bottom section. The bottom section 14 comprises a flat base 18 and an upright wall 20 around the edges of the bottom base 18. The base 18 has a cylindrical bearing hole 22 in the center thereof and an elongated bearing hole 24 therein adjacent the rounded corner. The upright wall 20 has an opening 26 theret-hrough at the rounded corner of the housing 12. Cover 16 has a downwardly extending rim 28 around its edges which is seated on the upright wall 20 of the bottom section. The cover 16 is secured to the bottom section 14 by a suitable cement. The inner surface of the cover 16 has a central cylindrical bearing hole 38 which is in alignment with the bearing hole 22 in the base 18, an elongated bearing hole 40 which is of the same shape as and is in alignment with the hole 24 in the base, and a third bearing hole 42 between and in radial alignment with the bearing holes 38 and 40.

A resistance element 44 is mounted on the base 18. As shown, resistance element 44 comprises a flat, circular disk 46 of an electrical insulating material, such as a plastic or ceramic. A narrow strip 48 of an electrical resistance material, such as carbon or a metal, is coated on the top surface of the disk 46 and extends in an annular path around the edge of the disk. The resistance strip 48 does not extend completely around the disk 46 but has ends which are slightly spaced apart. The disk 46 has a central hole 50 therethrough and an elongated hole 52 therethrough between the ends of the resistance strip 48. The central hole 50 is directly over the bearing hole 22 in the base 18, and the elongated hole 52 is of the same size as and is directly over the elongated bearing hole 24 in the base. Terminal wires 54 are connected to the ends of the resistance strip 48 by metal clips 56. The terminal wires 54 extend through an opening in the base 18 of the bottom section 14. The resistance element 44 could also comprise an annular core of an electrical insulating material having either a film of a resistance material coated thereon or a resistance wire helically wound therearound. Such a resistance element would be mounted on the base 18 and extend along the wall 29.

A main shaft 58 extends between the cover 16 and the base 18 of the bottom section 14. The ends of the shaft 58 are rotatably supported in the bearing holes 22 and 33. An annular flange 60 extends radially outwardly from the shaft 58 adjacent the base 18. An annular ring 62 circumscribes the flange 60 and is secured thereto by a radially extending rib 64. The outer diameter of the ring 62 is substantially equal to the outer diameter of the resistance I element 44.

A flat, annular contact 66 of an electrically conductive metal extends around the shaft 58 beneath the flange 69 and is secured to the flange so as to rotate therewith. A contact arm 68 extends radially outwardly from the contact 66 and downwardly toward the resistance strip 48. A contact finger 70 on the end of the contact arm 68 slidably engages the resistance strip 48. A collector member 72 of an electrically conductive metal is mounted on the resistance element disk 46 between the ends of the resistance strip 48. The collector member 72 has an elongated opening 74 therethrough which corresponds to the elongated opening 52 in the resistance element disk 46. An arm 76 extends radially inwardly from the collector member 72 and upwardly toward contact 66. A finger 78 on the end of the arm slidably engages the bottom surface of the contact 66. A terminal wire 80 is secured to the collector 72 and extends through the opening in the base 18 along with the terminal wires 54.

A drive shaft 82 extends between the cover 16 and the base 18 and is rotatably supported in the elon ated bearing holes 24 and 40. The drive shaft 82 extends along the inner periphery of the ring 62 and through the openings 52 and 74 in the resistance element disk 46 and collector 72 respectively. A drive wheel 84 extends around and is secured to the shaft 82. The drive wheel extends through the opening 26 in the housing wall 28 so that it is accessible from outside the housing 12 to permit rotation of the drive shaft 82. Drive shaft 82 has a pair of circumferential drive surfaces 86 and 88 above and below the drive wheel 84 respectively. The lower drive surface 88 extends within the ring 62 and is adapted to engage the inner periphery of the ring. A pair of springs 90 and 92 extend across the elongated bearing holes 24 and 40 respectively. The springs 90 and 92 engage the shaft 82 and press the shaft against the ends of the elongated bearing holes which are closest to the outer wall of the housing 12. This also holds the lower drive surface 88 of the shaft 82 against the inner periphery of the ring 62.

An idler wheel 94 is seated on the top surface of the drive wheel 84 between the drive shaft 82 and the main shaft 58. A stub shaft 96 extends upwardly from the idler wheel 94 and is rotatably supported in the third bearing hole 42 in the cover 16. The outer periphery of the idler wheel 94 is adapted to be engaged by the upper drive surface 86 of the drive shaft 82 and is adapted to engage a circumferential drive surface 98 on the main shaft 58. The drive surfaces 86 and 88 of the drive shaft 82, the inner periphery of the ring 62, the outer periphery of the idler wheel 94 and the drive surface 98 of the main shaft 58, are all of a construction which provides a driving connection between such mating drive surfaces when they are in mating relation. Such a driving connection can be either through frictional engagement of the mating surfaces or by providing such surfaces with suitable gear teeth.

In the operation of the variable resistor 10, the springs 90 and 92 normally urge the lower drive surface 88 into driving engagement with the inner periphery of the ring 62. Thus, when the drive wheel 84 is rotated to rotate the drive shaft 82, the ring 62 is rotated to rotate the main shaft 58. This rotates the contact 66 and moves the contact finger 70 along the resistance strip 48 to vary the resistance setting of the variable resistor 10. Since the diameter of the inner periphery of the ring 62 is much larger than the diameter of the drive surface 88 of the drive shaft 82, one rotation of the drive shaft 82 moves the contact finger 70 only a fraction of the total length of the resistance strip 48. Thus, a fine adjustment of the resistance setting of the variable resistor 18 can be obtained.

When the drive wheel 84 is pressed radially inwardly, the drive shaft 82 is moved along the elongated bearing holes 24 and 40 against the springs Q0 and 92 until the upper drive surface 86 engages the periphery of the idler wheel 94 and the idler wheel also engages the drive surface 98 of the main shaft 58. This also moves the lower drive surface 88 out of engagement with the inner periphcry of the ring 62. When the drive wheel 84 is rotated while holding it in its pressed-in position, the main shaft 58 is rotated by the drive shaft 82 through the idler wheel 94. Since the drive surfaces 86 and 98 of the drive shaft 82 and main shaft 58 are of substantially the same diameter, one rotation of the drive shaft will move the contact finger 70 along the entire length of the resistance strip 48. This provides a rough adjustment of the resistance setting of the variable resistor 19 which can be achieved quickly through a maximum of one turn of the drive wheel. Thus, by pressing in on the drive wheel 84 and rotating it, a large change in the resistance valve setting of the variable resistor 10 can be easily and quickly achieved, and by rotating the drive wheel 84 in its normal position, a fine adjustment of the resistance value setting can be achieved.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specifications as indicating the scope of the invention.

I claim:

1. A variable resistor comprising a housing having an enclosed cavity therein;

resistance element having an annular resistance path mounted in the cavity in the housing;

a shaft mounted in the cavity in the housing for rotation about the center of the annular resistance path;

a contact carried by said shaft and slidably engaging said resistance path;

a drive wheel rotatably mounted within the cavity and extending through the housing so as to be accessible for rotation from outside the housing;

means providing a first drive connection between the drive wheel and the shaft whereby rotation of the drive wheel rotates the shaft a fraction of the circumferential distance that the drive wheel is rotated;

means providing a second drive connection between the drive wheel and the shaft whereby rotation of the drive wheel rotates the shaft substantially the same circumferential distance that the drive wheel is rotated; and

said drive wheel being movable between a first position in which it drivingly engages the first drive means and a second position in which it drivingly engages the second drive means.

2. A variable resistor in accordance with claim 1 in which the drive wheel is mounted on a second shaft which is rotatably mounted within the cavity parallel to but spaced from the first mentioned shaft.

3. A variable resistor in accordance with claim 2 in which the first drive means includes an annular ring within the cavity and connecting with said first shaft, said ring being connected to the first shaft so as to rotate therewith, and means on said second shaft drivingly engaging the inner periphery of said ring.

4. A variable resistor in accordance with claim 3 in which the second drive means includes an idler wheel mounted between said two shafts for rotation about an axis parellel to said shafts, said idler wheel drivingly engaging both of said shafts when the drive wheel is in its second position.

S. A variable resistor in accordance with claim 4 in which the housing includes a base, an outer wall extending from the edge of the base and a cover spaced from and extending across the base and mounted on the wall, the resistance element is mounted on the base, the shafts extend between and are rotatab-ly supported in the base and the cover, and the drive wheel extends through the wall so as to be accessible for rotation.

6; A variable resistor in accordance with claim 5 in which the second shaft is supported in elongated bearing holes so as to permit the drive Wheel to be moved between its two positions.

7. A variable resistor in accordance with claim 6 including spring means engaging said second shaft and normally urging the means on said second shaft into driving engagement with the inner periphery of said ring.

8. A variable resistor in accordance with claim 5 in which the base of the housing is rectangular and has one rounded corner and the drive Wheel extends through the wall at the rounded corner.

References Cited UNITED STATES PATENTS 2,561,140 7/1951 Schoefer 338-121 2,629,799 2/1953 Hastings 338-l2lX 3,069,669 12/1962 Wapwer 338--121X 10 3,127,583 3/1964 Hudsonetal 338l3lX FOREIGN PATENTS 845,978 8/1960 Great Britain.

15 ROBERT K. SCHAEFER, Primw'y Examiner.

H. HGHAUSER, Assistant Examiner.

UNITED STATIQSFPATENT OFFICE CERTIFICATE OF CORRECTION.

g, te'ntNo. 3,388,365 June 11, 1968 George W. Wood It is certified that err patent and that said L shown below:

or appears in the above identified etters Patent are hereby corrected as In the heading to the' printed;

v ecification', line 4, p a." should read- "IRC, Inc, no., a corporation of Ohio Eiigned and sealed this 3rd' 'd ay of March 1970.

st: O 1rd M. Fletcher, Jr. J sting Officer Commissioner of Patents 

